Atomic layer deposition (ALD) is a deposition process used to form thin layers on complex structures found in many advanced semiconductor devices. The general steps of the ALD process are well known and typically consist of i) exposing the substrate to a precursor pulse to form a monolayer of the precursor on the surface; ii) purging unreacted precursor from the system; iii) exposing the substrate to a reactant (i.e. usually an oxidant) pulse to form a layer of material on the substrate; iv) purging unreacted reactant from the system; and v) repeating steps i)-iv) until a layer of the desired thickness is formed.
Ideally, the exposure of the substrate to the precursor pulse forms a saturated, self-limiting monolayer on the surface. This has the added benefit that the growth of the layer will be conformal. This benefit makes ALD processes especially useful for depositing thin layers on complex structures found in many advanced semiconductor devices. Because of the self-limiting nature of the deposition, the conformality is expected to be approximately 100% and the deposition should be insensitive to pressure. However, in practice, the conformality is not 100% and the deposition rate is observed to vary as a function of pressure. Therefore, systems and apparatus are needed to efficiently evaluate and characterize the deposition of materials using an ALD technique as a function of different process parameters.